Yeah, but how many of those scenarios result from perfect play on both sides?
Well, nobody can say about perfect play, of course: we aren't close to that level. In practice draws are quite rare, perhaps in the neighborhood of 1% of games.
I think the most common draw hinges around Blastforge, actually, not Wall: you've breached me and killed off most of my Tarsiers, but I get one last attack with them to reduce you to 2 or fewer damage yourself; eventually, you can kill everything but my Blastforge.
As an example of how a game can end in a draw, see
Rrkgn-aQJpa. This one was actually a win (I don't recall ever getting an actual draw, and it's impossible to search for one to see if I'm wrong), but if I'd made one more health worth of mistakes, my opponent's last Grimbotch would have killed my Cynestra and then timed out, leaving neither of us any attackers or income at all.